Electro-optically active organic diodes are for example used as organic light emitting diodes (OLEDs), in lightning devices, in display devices and in organic solar cell devices. An organic diode in an organic solar cell device is arranged to generate electricity from light, whilst in a lightning device, the organic diode is arranged to generate light from electricity. Nevertheless, these are just different manifestations of common fundamental properties pertaining to certain electro-optically active organic materials. Progress and development in one area, such as in the area of lightning devices and OLEDs, thus can be utilized for improvements in the other area, such as in the area of organic solar cell devices.
This far, efforts mostly have been spent on lightning devices, and in particular on OLEDs. This is partly owing to that the obtainable efficiency, reliability and operational lifetime so far have been considered too poor for viable organic solar cell devices, especially in light of what can be achieved in conventional solar cell devices. Although these properties are desirable to improve also in the area of lightning application devices, the requirements are often not fully as high, and there are already commercially available products, such as displays based on OLED technology. Partly, this is owing to that OLEDs emit light and thus do not require backlighting such as in conventional liquid crystal displays (LCDs). Some other advantages of electro-optically active organic diodes in general are for example that they are comparatively easy and cost efficient to make, can be fabricated in thin, flexible layers and even be made transparent.
Recently there has been progress in efficiency by use of highly doped organic semiconductor materials, in particular for use as charge carrier layers, such as transport layers in OLEDs.
For example, US 20050040390 presents doped organic semiconductor materials that can be used to improve OLEDs. The materials have enhanced charge carrier density and effective charge carrier mobility. The doping is achieved by doping an organic semiconductor material with organic molecules, which, for example, allow doping of polymer layers with large, non-mobile molecules.
Further, US 20060033115 discloses a transparent light emitting organic diode component using highly doped organic layers as transport layers for holes and electrons. The transport layers are arranged adjacent to electrodes. Dopants are organic molecules with molecular masses above 200 g/mole. Doping concentrations are in the range between 1:10 and 1:10000.
Although highly doped organic semiconductor layers and materials indeed look promising and can result in great efficiency improvements and very power efficient devices based on electro-optically active organic diodes, problems with reliability is a remaining problem and can be an obstacle for commercial success of devices employing these layers and materials.